The concept of the present invention is concerned with the computation of the radar or sonar ambiguity function employing electro-optical techniques and means as well as similar mathematical computations.
There is an increasing tendency to employ sophisticated waveforms using various forms of amplitude, phase, and frequency codings in modern radar technology. Classification schemes presently used in EW measure only the most elementary radar properties such as frequency band, pulse length, pulse repetition rate and scan rate. These characteristics are often sufficient to identify many specific radars by comparison with previously established reference libraries, but they do not allow the deduction of the radar's full capabilities. Therefore, if a radar signal is encountered in the field for the first time, little can be said about the detailed system's capabilities or the countermeasure techniques which would be optimally effective.
The ambiguity function proves to be an indispensable tool for radar and sonar signal designers. If the ambiguity function of an unknown signal could be calculated with a compact system in real time or near real time, a completely unknown radar could be characterized and optimally countered in the field. Prior to the present invention, however, there has been no teaching to verify that the strong potential of an electro-optical approach can be achieved in this case.
The power of optical analog information processing and computing is attributed to the fact that optical systems are capable of processing information in parallel at very high rates with relatively few components but usually with only moderate accuracy. By comparison, electronic processing systems offer high precision but at the expense of complex-sophisticated components that are intrinsically serial in nature. Optical processing systems are usually subdivided into two main categories, coherent and incoherent. Coherent optical systems use coherent light for purposes of information processing. These systems are linear in amplitude and are capable of manipulating both the amplitude and phase of the light disturbance. However, coherent systems are highly sensitive to vibration and therefore must be isolated from the environment in most practical applications. The result is often large, complex systems mounted on granite slabs which can be only employed in a ground-base activity. Incoherent optical processing systems, on the other hand, utilize incoherent light and are linear in intensity. As a result, these systems are more compact in size and weight and can be easily utilized in an environment such as that found aboard ship or aircraft.
Incoherent optical processing systems have been designed in the past, examples of which are illustrated in U.S. Pat. Nos. 3,937,942 and 4,009,380 incorporated herein by reference. The U.S. Pat. No. 3,937,942 describes an electro-optical correlator. The U.S. Pat. No. 4,009,380 describes an electro-optical system for performing a wide variety of matrix-vector multiplications. Neither of these designs, however, can compute the ambiguity function.
Accordingly, it is desirable that the advantageous aspects of electro-optical techniques be availed of to perform the radar or sonar ambiguity function computation or other mathematical computations of a similar form.